(1) Field of the Invention
The present invention relates to a plastic laminate. More particularly, the present invention relates to a plastic laminate structure comprising a layer of a creep-resistant resin represented by polyethylene terephthalate and a gas barrier layer of an olefin-vinyl alcohol copolymer, which are tightly bonded to each other through a copolyester type adhesive layer. Furthermore, the present invention relates to a multi-layer plastic vessel which is excellent in the combination of the gas barrier property, creep resistance, rigidity, impact resistance, heat resistance, interlaminar peel strength and transparency and is valuable for sealing and storing contents such as foods for a long time.
(2) Description of the Prior Art
Polyethylene terephthalate is excellent in moldability and mechanical properties such as creep resistance and can be molecularly biaxially oriented. Accordingly, polyethylene terephthalate is widely used for a light-weight plastic vessel, especially a bottle for a drink, which is excellent in such properties as creep resistance, impact resistance, rigidity, gas barrier property, light weight characteristic, heat resistance and transparency. However, the gas permeability of this polyester bottle is still higher than that of a glass bottle and cannot be neglected. For example, it is said that the shelf life of a small polyester bottle having an inner volume smaller than 1 litter, which is filled with a carbonated drink such as cola, is about 2 months at longest.
An olefin-vinyl alcohol copolymer such as a saponified ethylene-vinyl acetate copolymer is known as a heat-formable resin excellent in the oxygen barrier property, and it also is known that this resin is combined with an olefin resin excellent in the moisture resistance and the laminate is used for the production of an undrawn or drawn multi-layer plastic vessel.
Formation of a vessel from a laminate structure comprising a polyester layer and an olefin-vinyl alcohol copolymer layer has already been proposed. It is naturally expected that this laminate structure will be excellent in the combination of the gas barrier property, creep resistance, heat resistance, impact resistance and rigidity, but this laminate structure has not practically been used for a vessel, especially a biaxially drawn blow-formed vessel. The reason is considered to be that a thermoplastic adhesive capable of forming a strong interlaminar bond between a polyester and an olefin-vinyl alcohol copolymer has not been found out.